Implement "Save image as" for canvas (chromium side).

chrome/browser/renderer_context_menu/context_menu_content_type.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_RENDERER_CONTEXT_MENU_CONTEXT_MENU_CONTENT_TYPE_H_
 #define CHROME_BROWSER_RENDERER_CONTEXT_MENU_CONTEXT_MENU_CONTENT_TYPE_H_
 
 #include "chrome/browser/custom_handlers/protocol_handler_registry.h"
 #include "content/public/common/context_menu_params.h"
 #include "ui/base/models/simple_menu_model.h"
@@ skipping 20 matching lines @@
   // Order matters as they are appended in the enum order.
   enum ItemGroup {
     ITEM_GROUP_CUSTOM,
     ITEM_GROUP_PAGE,
     ITEM_GROUP_FRAME,
     ITEM_GROUP_LINK,
     ITEM_GROUP_MEDIA_IMAGE,
     ITEM_GROUP_SEARCHWEBFORIMAGE,
     ITEM_GROUP_MEDIA_VIDEO,
     ITEM_GROUP_MEDIA_AUDIO,
+    ITEM_GROUP_MEDIA_CANVAS,
     ITEM_GROUP_MEDIA_PLUGIN,
     ITEM_GROUP_MEDIA_FILE,
     ITEM_GROUP_EDITABLE,
     ITEM_GROUP_COPY,
     ITEM_GROUP_SEARCH_PROVIDER,
     ITEM_GROUP_PRINT,
     ITEM_GROUP_ALL_EXTENSION,
     ITEM_GROUP_CURRENT_EXTENSION,
     ITEM_GROUP_DEVELOPER,
     ITEM_GROUP_DEVTOOLS_UNPACKED_EXT,
@@ skipping 24 matching lines @@
 
   const content::ContextMenuParams params_;
   content::WebContents* source_web_contents_;
   Profile* profile_;
   const bool supports_custom_items_;
 
   DISALLOW_COPY_AND_ASSIGN(ContextMenuContentType);
 };
 
 #endif  // CHROME_BROWSER_RENDERER_CONTEXT_MENU_CONTEXT_MENU_CONTENT_TYPE_H_